Answer :

You can get seven from substracting 16 and 9. We know that 16 = 4² and 9 = 3², so what you're looking for is 4² - 3² = 7.

I hope it will help you :-)
frika
Let x be first number and y- second number. When you subtract first square number from second you get [tex]y^2-x^2[/tex] and it is equal to 7.

Hence
[tex]y^2-x^2=7[/tex].

Find factors of right and left sides:[tex](y-x)(y+x)=1\cdot 7[/tex].

Since [tex]y+x\ \textgreater \ y-x[/tex] you have that  
[tex] \left \{ {{y-x=1} \atop {y+x=7}} \right. [/tex].
Add these equations: 
[tex]y-x+y+x=1+7, \\ 2y=8, \\ y=4[/tex].
Then x=7-y=7-4=3.
Answer: [tex]4^2-3^2=7.[/tex]

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